Oxytocin Analogues with O-Glycosylated Serine and Threonine in Position 4

Oxytocin structure was modified in position 4 using glycoamino acids. Procedure for transformation of Fmoc-protected serine and threonine derivatives into appropriate 0-glycosylated precursors suitable for solid phase peptide synthesis (SPPS) was worked out. The α- and β-O-glycosides were synthesized from Fmoc-serine and Fmoc-threonine allyl esters and appropriate glycosyl bromide using Hanessian's modification of the Koenigs-Knorr reaction. These N α -Fmoc-protected glycoamino acids were used in the synthesis of glycopeptides. Eight analogues of oxytocin were prepared. The obtained glycopeptides were tested for their rat uterotonic in vitro, pressor and antidiuretic activities and for their affinity to human oxytocin receptor. Moreover their stability towards α-chymotrypsin cleavage was studied.